Add an option to start the first window of a workspace in stacked mode

[ascesh]

Hey!

Looking for a way to start every workspace in stacked mode.
this helps in low res screens, laptops where it make sense to only to split the window into two , any further the window sizes get too small to be usefull.

I find myself splitting the window into two(in my low res laptop screen), starting stack mode on both, then piling on the windows in both the stacks..
this keeps the window sizes constant (half a screen), yet still lets me manage a large number of active windows.

this can be optional of course - as some would prefer to start in tiling mode and stay in tiling mode.

Impressed how close the extension makes gnome feel like i3!
the feature idea is much like workspace_layout stacking in i3 ;)

~ascesh